public static Bitmap base64StrToBitmap(String base64Str) {
    if (base64Str == null || base64Str.isEmpty()) return null;
    java.util.Base64.Decoder decoder = Base64.getDecoder();
    byte[] decodedBytes = decoder.decode(base64Str);
    return BitmapFactory.decodeByteArray(decodedBytes, 0, decodedBytes.length);
}

• 在 Android 开发中，执行上述代码，传如有效的 Base64 字符串 data:image/png;base64,iVBORw0KGg...，报如下错误

Caused by: java.lang.IllegalArgumentException: Illegal base64 character 3a

问题原因

1. 3a 是字符 : 的 ASCII 码，出现在 Base64 字符串的 data:image/png;base64, 这部分前缀中

2. decoder.decode 方法只能解析纯 Base64 部分的数据，即逗号（,）之后的内容

处理策略

• 在解码前，先检查并移除 Base64 字符串的前缀

public static Bitmap base64StrToBitmap(String base64Str) {
    if (base64Str == null || base64Str.isEmpty()) return null;

    if (base64Str.contains(",")) {
        base64Str = base64Str.split(",")[1];
    }

    java.util.Base64.Decoder decoder = Base64.getDecoder();
    byte[] decodedBytes = decoder.decode(base64Str);
    return BitmapFactory.decodeByteArray(decodedBytes, 0, decodedBytes.length);
}

问题观察

1. 问题复现：传入带前缀的 Base64 字符串，程序报错

String base64Str = "data:image/png;base64,iVBORw0KGg...";

java.util.Base64.Decoder decoder = Base64.getDecoder();

byte[] decodedBytes = decoder.decode(base64Str);

Log.i(TAG, "decodedBytes length: " + decodedBytes.length);

Bitmap bitmap = BitmapFactory.decodeByteArray(decodedBytes, 0, decodedBytes.length);

Log.i(TAG, "bitmap: " + bitmap);

# 输出结果

Caused by: java.lang.IllegalArgumentException: Illegal base64 character 3a

2. 问题处理：传入不带前缀的 Base64 部分的字符串，程序正常运行

String base64Str = "iVBORw0KGg...";

java.util.Base64.Decoder decoder = Base64.getDecoder();

byte[] decodedBytes = decoder.decode(base64Str);

Log.i(TAG, "decodedBytes length: " + decodedBytes.length);

Bitmap bitmap = BitmapFactory.decodeByteArray(decodedBytes, 0, decodedBytes.length);

Log.i(TAG, "bitmap: " + bitmap);

# 输出结果

decodedBytes length: 36251
bitmap: android.graphics.Bitmap@9a78bbe